Wafer inspection systems that allow an entire wafer to be scanned for defects are known. Such systems typically utilize a laser beam which is scanned across the surface of the wafer. If the reflected laser beam deviates from the expected intensity for a given wafer location, that location is flagged for further scrutiny. After the entire wafer surface has been scanned, a white light imaging system may be used to review individual areas which were flagged during the laser scan process. The white light images of the areas in question may be reviewed by an operator of the imaging system, who may classify the areas according to the type of defect or anomaly found, if any. Alternatively, an automatic defect classification system may be used to gather an image of each potentially defective area and electronically process the image to determine a classification of the area. The classifications of the reviewed areas, whether accomplished by a human operator or an automatic defect classification system, may be used to accept or reject the wafer for further processing, and to determine whether any of the preceding wafer fabrication processes is producing systematic defects.
In "flip chip" or ball grid array packaging, an array of solder bumps, such as controlled collapse chip connection (C4) solder bumps, is deposited on the surface of the wafer to establish electrical contacts with corresponding areas on the package. Prior to packaging, the solder bumps on the wafer should be inspected to ensure accurate placement, size and shape of the solder bumps. However, the laser scanning method outlined above is not suitable for inspection of and classification of defects in the solder bump array. Furthermore, manual review of white light images of the entire wafer surface to inspect the entire solder bump array would be extremely slow and expensive.